A high pressure discharge lamp, such as a metal halide, mercury or high pressure sodium lamp, is typically powered by an electromagnetic ballast circuit incorporating an iron core. The ballast transformer receives voltage from a power source, and outputs a ballast voltage for driving the lamp. The ballast circuit, which uses the iron core to achieve the necessary voltage adjustment, represents a major component of ballast cost, as well as bulk. The foregoing type of ballast circuit typically suffers the problem of powering only a single high pressure lamp. It would be desirable to more efficiently utilize a ballast circuit so that it simultaneously powers plural (e.g. dual) high pressure gas discharge lamps and realizes a considerably reduced per-lamp ballast cost and improved ballast efficiency.